It is important for the desired operation of a transit vehicle door control system to know when the vehicle has reached a predetermined zero speed of operation, such that the vehicle doors can be opened at the proper time to permit the safe movement of passengers to and from the vehicle.
It is known to determine a defined zero speed of a vehicle for the purpose of door opening control in response to signals provided from the wayside, as disclosed in U.S. Pat. No. 3,958,783 of R. S. Rhoton.
It is known to employ a programmed computer control system responsive to a tachometer established zero speed signal which enables door open signals provided at both the front end and the rear end of a train for determining the opening of the doors when the train is positioned as desired, as disclosed by U.S. Pat. No. 4,269,377 of D. L. Rush et. al.
It is known to sense a vehicle slip-slide condition and to control a vehicle in accordance with that condition as disclosed in U.S. Pat. No. 4,392,091 of R. D. Roberts et al.